1. Field of The Invention
This invention relates to connecting clips which are used in the formation of junctions for elongate reinforcing members, such as metal rod and reinforcing members, to form extended grids. These grid may be provided with means for cathodic protection which restricts corrosion and increases the useful life of reinforced concrete structures by stabilizing the metal grid.
2. Description of The Related Art
Metal rods in the form of a grid structure have long been used as internal reinforcement for concrete structures, such as beams, girders, columns, support surfaces and the like. These concrete forms are frequently subject to weakening due to the gradual deterioration of the reinforcing metal grid. Deterioration of the grid occurs because most metals, exposed to natural environments without protection, enter into reaction with constituents in the environment. This reaction results in the formation of corrosion products typical of the ores from which the metals were originally formed. Thus constituents, present in concrete, will attack the metal reinforcing structure, especially in the presence of moisture and soluble salts. This phenomenon may also be referred to as electrochemical corrosion. Since moisture is readily absorbed by concrete, it is necessary to provide a means of protection for the metal reinforcement. Two such means are regularly practiced. The first involves the deposition or formation of a protective coating on the surface of the metal rod which is used to form the grid structure. Coatings applied to rods are effective in protecting them from environmental attack. Unfortunately, damage of the coating is common and results in voids, cuts or scratches which allow access to the metal causing it to dissolve via electro-chemical corrosion. The dissolution of a metal in a liquid environment occurs at discrete sites which act as anodes. A corrosion cell consists of an anode and a cathode in contact with each other and with a common electrolyte. The metal forming the anode will dissolve while the cathode remains intact. It is necessary, therefore, to provide means whereby the metal to be protected becomes the cathode under conditions of corrosion cell formation. There are several ways of doing this. The most commonly used method is to attach a sacrificial anode to the metal to be protected. This method relies upon a characteristic electromotive force (EMF) which controls the tendency of a given metal to corrode. If two metals are connected through an external conductor and there is provision for a continuous electrolyte, the metal with the lower EMF will corrode.
An alternate means of cathodic protection is impressed-current cathodic protection (ICCPS). In this case the negative terminal of a DC power source is connected to the metal grid and the positive terminal is connected to a suitable anode adjacent to the reinforced structure. This arrangement establishes an electrical bias by which the reinforcing grid becomes the cathode upon formation of a corrosion cell.
U.S. Pat. No. 3,553,094 (I. C. Scott Jr.) discloses a device which may be strapped onto a coated pipe to provide a metallic component which preferentially becomes the anode during electrolytic cell formation in the presence of moisture. Penetration of the protective coating of the pipe occurs during tightening of the device against the pipe. Sharp projections, in contact with the protective pipe coating, cut through the coating and penetrate the metal surface to provide metal-to-metal, electrical connection to the pipe. A sacrificial anode, attached to the device, will be preferentially consumed, via electrochemical action, leaving the metal pipe intact.
Another form of sacrificial anode is revealed in U.S. Pat. No. 4,855,024 (Drachnik et al). In this case the anode is produced in the form of a mesh. The mesh is constructed of elongate electrodes held together at points of intersection or junctions by resilient conductive clips which secure and electrically connect the elongate electrodes. When suitably connected to e.g. a reinforcing grid of steel the mesh anode will protect the steel grid from corrosion. Protection is achieved by connecting the steel grid to a mesh anode positioned at the surface of the concrete form or embedded in concrete closely proximate the grid.
The properties and form of the resilient conductive clips, used to develop and stabilize the mesh anode, are selected to provide long term, optimum connection at the junctions.
Methods involving the use of clips to form grid networks are disclosed in U.S. Pat. Nos. 3,778,951 and 3,863,416 (both by G. Oroshakoff). In neither case is consideration given to corrosion protection of the metal rods used to form grids of the invention.
Study of the prior art has not revealed any concept which provides protective coating and cathodic protection combined with ease of assembly of metallic grids using connecting clips of this invention.